The present invention relates generally to materials and methods useful in the detection of antibodies and particularly relates to a novel, soluble, rubella virus antigen. The antigen of the invention is employed to develop specific immunoassay reagents useful for rapid detection and quantification of rubella antibodies in test fluids. Materials and methods of the present invention are useful in establishing the immunological status of a patient, (e.g., a woman of child-bearing age) and are also of value in diagnostic programs.
Procedures commonly employed for determination of anti-rubella antibodies in test fluids are based upon antibody inhibition of baby chick erythrocyte hemagglutination by an insoluble rubella virus particle. Among the essential steps of such procedures is the absorption of test fluids with kaolin to effect removal of non-specific lipoprotein inhibitors and absorption of the sera with baby chick erythrocytes to remove cross-reacting antibodies present in the fluid all prior to testing agglutination inhibition. Hemagglutination inhibition (HAI) assays of this type are relatively reliable but are time consuming because of the above-mentioned serum pre-treatment steps. Final test results are ordinarily not available for at least about 5-7 hours after test fluid collection. Other techniques for detection of antibody to rubella are summarized, e.g., in Meyer, H. M., et al., Am. J. Chin. Pathol., 57: 803-813 (1972).
Prior attempts have been made to secure a soluble rubella virus antigen, apart from the insoluble hemagglutinins used in HAI tests. The art describes identification of two major "soluble" antigens (designated theta and iota) but attempts to definitively isolate and characterize these antigens from rubella-infected cell cultures have met with limited success and no soluble antigen heretofore isolated has been useful in developing an antigen-sensitized particle effective in detection and quantification of antibodies to rubella.